Plasma cleaning or etching is a process whereby a gas is subject to a radio frequency electric field in a reaction chamber to form a plasma. A plasma is a gas which contains positive, negative and neutral atoms, electrons and/or molecules including radicals and a "gas" of emitted photons. A chemically inert gas, such as argon, is ionized to form the plasma and accelerated to impinge on a device structure so that material is removed from the surface of the device structure by momentum transfer, a process similar to sand blasting. The ions/radicals interact with the surface of the atoms or molecules within the material to be cleaned or etched and in some circumstances forming a volatile by-product which is subsequently removed from the reaction chamber.
One form of cleaning uses a high density plasma source for bombarding the device structure. High density plasma cleaning utilizes a lower direct current (DC) offset voltage to accelerate the ionized particles toward the device structure than conventional plasma cleaning techniques. The lower offset voltage allows for cleaning with less chance of device damage often caused by high energy ion impacts.
Sputter deposition refers to a mechanism in which atoms are dislodged from a target material by collision with high energy particles. The sputtering process involves generating and directing ions at a target. The momentum of ions incident on the target is transferred to the surface atoms of the target material, causing their ejection. A portion of the ejected sputtered species from the target are accelerated in an electric field toward a device structure, although the vast majority of the sputtered species are neutral. The ejected atoms from the target condense on the surface of the device structure to form the desired film.
Cleaning and sputter deposition are typically performed in separate chambers requiring the device structures to be moved from chamber to chamber. Handling of the device structures may expose them to contamination, the formation of native oxide thereon, or damage, and generally requires an extra chamber.